13.3.12 Replacement Models
There are generally two types of replacement problems, namely:
(1) renewal of items that wear out or depreciate with time and
(2) those that do not wear out, but fail suddenly.
The first category comprises items such as equipment, machines, vehicles, uniforms, etc. The problem resides in determining the optimum time for replacement,
such that the overall cost of new equipment, the cost of maintaining the old
equipment efficient and the cost of efficiency loss is a minimum. Solutions to such
problems are found by calculus and dynamic programming.
The second category comprises items such as tyres, electric bulbs, etc. The
problem resides in determining
(a) which items to renew or replace
(b) whether to renew or replace them in groups or not and,
(c) if yes, when.
The objective in this second category is to minimise the overall cost of the item,
the replacement cost and the failure associated cost.
13.3.13 Heuristic Models
Heuristic models practise rules of thumb or instinctive rules and guidelines (often
under computer control) to reconnoitre the most probable paths, while making
educated guesses in reaching a problem’s solution. Here, it is not necessary to
check all the possible alternatives, to obtain the optimum one. Heuristic models
seem sufficiently promising for future OR work, as they link strictly analytical
formulations with the managers’ usual operating principles.
13.3.14 Goal Programming
Goal programming quite resembles linear programming, but applies to situations
where there are multiple goals or objectives. For example, a company producing
stone aggregates and concrete blocks, may have the following objectives:
(1) maximize profit in rupees,
(2) maximize tonnage of aggregates production,
(3) maximize number of concrete blocks to be manufactured.
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There are generally two types of replacement problems, namely:
(1) renewal of items that wear out or depreciate with time and
(2) those that do not wear out, but fail suddenly.
The first category comprises items such as equipment, machines, vehicles, uniforms, etc. The problem resides in determining the optimum time for replacement,
such that the overall cost of new equipment, the cost of maintaining the old
equipment efficient and the cost of efficiency loss is a minimum. Solutions to such
problems are found by calculus and dynamic programming.
The second category comprises items such as tyres, electric bulbs, etc. The
problem resides in determining
(a) which items to renew or replace
(b) whether to renew or replace them in groups or not and,
(c) if yes, when.
The objective in this second category is to minimise the overall cost of the item,
the replacement cost and the failure associated cost.
13.3.13 Heuristic Models
Heuristic models practise rules of thumb or instinctive rules and guidelines (often
under computer control) to reconnoitre the most probable paths, while making
educated guesses in reaching a problem’s solution. Here, it is not necessary to
check all the possible alternatives, to obtain the optimum one. Heuristic models
seem sufficiently promising for future OR work, as they link strictly analytical
formulations with the managers’ usual operating principles.
13.3.14 Goal Programming
Goal programming quite resembles linear programming, but applies to situations
where there are multiple goals or objectives. For example, a company producing
stone aggregates and concrete blocks, may have the following objectives:
(1) maximize profit in rupees,
(2) maximize tonnage of aggregates production,
(3) maximize number of concrete blocks to be manufactured.
366
13 Modelling in Infrastructure Planning